It has been shown that dietary supplementation with arginine plus glycine and with the trace minerals zinc, copper and manganese reduces post-trauma nitrogen loss in young rats. It has further been shown that the protein needs of old rats differ in some aspects from those of mature ones. Using the same animal models it will be studied whether the above mentioned post-trauma effects of nutritional intervention are additive and whether they will also be operative in mature and old rats. In further experiments the type of anesthesia used in order to cause trauma, the environmental temperature and branched-chain amino acid supplementation will be additonal variables. In order to study whether nutrient needs can be shown to differ with age on the cellular level, the amino acid requirements for growth as well as for maintenance of kidney cells from rats of different age will be determined in primary cell cultures. Attention will first be directed to amino acids that have been shown to be essential in vitro but not, at least with adult rats under normal conditions, in vivo. These include arginine, histidine, tyrosine, cystine and glutamine. The overall objective is to minimize nitrogen losses after injury or surgery in aged individuals and to gather information of the metabolic events involved in recovery from injury.